Spectroscopic investigation of impurities in FTU

Summary form only given. In order to assess the contribution of impurities to Zeff in the FTU high-field tokamak, a quantitative determination of the impurity sources has been made by measuring visible line emission of the most relevant elements in the FTU. Visible spectra observed along chords looking at the plasma in the proximity of the wall have been compared to those observed through an endoscope system. Concentrations of impurities in the bulk plasmas have been obtained by simulations with a transport code of vacuum ultraviolet line intensities due to ions existing in inner plasma regions. Correlating the incoming fluxes to the concentrations in the bulk plasma at various plasma densities indicates that the penetration of impurities is less efficient at low densities. The addition of extrinsic impurities, either metallic or gaseous, by different techniques (laser blow-off, metallic sublimiters, gas puffing) allows a better estimation of the transport of impurities.